Wednesday, September 2, 2009

Thinkpad T40

Customer arrives with IBM Thinkpad T40 stating that it will work from a charged battery. But it will not work with known good AC Adapter.

Problem:Works on battery, will not work on AC Adapter

The problem is caused by 2 things in this case. First the Toshiba TPC8014 MOSFET was reading bad when I checked it with a meter. After I replaced it, the unit was only supplying 10.4v to the charge section of the board. Which is not enough to trigger the adjacent mosfet to supply power to the charge section. So then; checking the Fuse [F2] found that it was blown (open circuit), most likely by the MOSFET being shorted. click on picture to see larger view

Solution:Replace MOSFET TPC8014, replace fuse.

The MOSFET:30V N-Channel MOSFET ~11a max rating

Exact Replacement:Toshiba TPC8014comment: The funniest wording of what happens under constant use.Using continuously under heavy loads (e.g. the application of high temperature/current/voltage and the significant change in temperature, etc.) may cause this product to decrease in the reliability significantly even if the operating conditions (i.e.operating temperature/current/voltage, etc.) are within the absolute maximum ratings.To me this translates as. If this MOSFET is used continously under heavy loads it will stop working or properly (like: your computer being ON all day). In technical terms "It Will Break".

Notices:When replacing the MOSFET, be careful not to use too much solder or you may short exposed pads under the chip (This is a typical practice of the Chinese board manufacturers to keep unskilled techs oblivious and discourage them from repairing at the component level. Computer techs eventually buy another motherboard where electronic techs fix them). Again, this is my opinion because that is not a test point under the chip and you do not have access to it under a normal repair situation. If you are not be skilled enough at micro soldering, you can pre-insulate the holes with a small piece of mylar tape to prevent solder from bridging the holes before replacing the MOSFET.Since it was an easy solution, I am trying to be as clear as possible with the solution and the diagnosis.

Do you have any suggestions or comments for replacing an F2 fuse? It's been a long time (10 years or so) since I've done any soldering projects, and wanted to hear from an expert about this. I'm just a young man who hasn't done any hobby work in a while and some guidance would be much appreciated...

If you have to replace the fuse, then make sure you have some tweezers, flux, and a small tip soldering iron. If you cannot get that close, you may want to try a heat gun ~500 degrees (no higher). The motherboard will have to be removed from the case, so you don't melt plastic, and don't go above the temp above, because the DC IN connector will melt.

The fuse is small and I had trouble getting it, so I just took one off of another T40 parts board. You know, the ones you keep that are 'dogs' and no chance of repairing. Like spills and other maladies.

I have similar problem with R50.The board looks the same, but i found out thet the cmos batt was empty, and as soon as you plug the power nothing happens.On MOSFET that was here replaced is on both sides 16,5V from power supply and on the one on right which connects battery is also on one side 16,5V and on other is battery voltage which is 11,2V. Now i dont know what is the charged battery voltage (batt is rated cca 10,8V).So the notebook is dead at the moment and i dont know what to do.Any suggestions?thanks Dusan

- Laptop works perfectly using the battery- When used with the power adapter with or w/o batt, it failed to boot sometime. If it did boot to Windows, it will hang after awhile.- The batt can charge when inserted into the laptop- F2 fuse is OK

About Me

Hoosier Newman is known as the Laptop Doctor in Charlotte. More of a hobby that got out of hand than a business. Since I am thoroughly familiar with computers it is a deviation from the ordinary. See my profile in my blog for additional notes ...